Hydrocolloid adhesives for skin applications are well known in the art.
Hydrocolloid adhesives for skin applications have attractive features in terms of moisture absorption and price. However, hydrocolloid adhesives tend to be rough on the skin, and when such adhesives are removed from the skin, the skin may be stripped of its upper layer. Changing the adhesive repeatedly as would be the case for e.g. ostomy appliances leaves the skin damaged and severe pain may be associated with the removal of the adhesives. The problem can to some extent be handled by using softer adhesives that deforms more during peeling. When the deformation is larger, the area over which the peel force is transmitted to the skin becomes broader leaving the skin less stressed compared to a harder adhesive with the same peel force. On the other hand, increasing the softness of the adhesive by modifying the chemical composition thereof may reduce the structural integrity of the adhesive and the adhesive may fail cohesively.
It has now been found that a larger deformation of the same adhesive when peeling with the same peel force may be achieved by eliminating or reducing the incompressibility restriction imposed by the solid adhesive by introducing small bubbles of gas that are able to expand when internal pressure reduces because of peel deformation of the adhesive mass.
In this way, the adhesive mass is still incompressible in a differential fluid element but in a local scale of the size of the included bubbles, the adhesive mass is compressible and able to expand with the given flow.
Introduction of bubbles into an adhesive lowers the modulus of the adhesive and makes it softer and more flexible. An adhesive comprising bubbles will have a lower bending resistance than its incompressible counterpart. This will improve wear comfort.
A foamed adhesive is also more impact resistant and has a cushioning effect, because a soft foamed adhesive is able to distribute loads better and improve pressure relief.
A disadvantage of the observed in a foamed adhesive is that surface tension tends to merge bubbles together, leading to larger bubbles. The density may also increase if bubbles merge with the surface of the adhesive.
Porous or foamed hydrocolloid adhesives for medical applications have already been described in the art.
Thus, U.S. Pat. No. 4,775,374 describes a skin barrier for use by ostomates. The barrier makes use of a porous layer of hydrocolloid adhesive with holes or pores having a size 10-300 μm. The foamed adhesive layer is thin compared to the bubble size 1-10 mils (corresponding to 25.4-254 μm) and this construction creates open pores for gas transport through the adhesive layer. The gas transport in these adhesives should be within 1-100 cm3/sec/in2 according to ASTM D-726-71.
The foamed adhesive body of the present invention differs from the adhesives described in U.S. Pat. No. 4,775,374 in that the foam is closed celled and without interpenetrating cavity structure. Furthermore, the average cell diameter of the gas bubbles in the adhesive body of the invention is limited to a narrow range of diameters providing the necessary compressibility.
U.S. Pat. No. 6,326,524 describe foamed hydrocolloid adhesives with a bubble size of 200-4000 μm. It is said that the foamed structure of the adhesive improves absorbency, enables transmission of moisture through the adhesive, increases flexibility and lowers product cost. The bubble size is limited to be in the regime 200-4000 μm. The adhesive used in the example has been tested and was found to be very hard.
The foamed adhesive body of the present invention differ from the adhesives described in U.S. Pat. No. 6,326,524 in that the average diameter of the gas bubbles in the adhesive of the present invention is much smaller and the adhesive body is considerably softer which provides the desired broad peel front. Large bubble diameters may compromise cohesion of the adhesive body during peeling.
WO 2004/080498 also suggests absorbent polymer compositions in the form of foams of a pressures sensitive hydrocolloid adhesive. There is no information as regards the average diameter of the gas bubbles in these materials.
The foamed adhesive body of the present invention differs from the adhesives described in WO 2004/080498 in that the bubbles in WO 2004/080498 is created using expandable microspheres. These bubbles are hard as they are incapsulated in a hard material even after expansion. Thus, such an adhesive would not provide the necessary compressibility described in this patent.